1. Field of the Invention
The present invention relates to a portable timepiece in which a crown is held so as not to be carelessly rotated by utilizing mesh of screws and a method of fabricating a crown provided to the timepiece.
2. Description of the Related Art
In a background art, there is a portable timepiece including a screw lock structure for holding a crown so as not to be rotated carelessly by utilizing mesh of screws. According to the screw lock structure, the crown includes a crown shaft for cooperatively moving a hand setting stem and a crown head for rotating the shaft. Further, a shaft end portion of the crown shaft is arranged at outside of a pipe having a male screw portion and fixed to a case band. Along therewith, a peripheral portion of the shaft end portion is formed with a rotational force receiving portion of a deformed shape and the crown head is provided with a female screw portion and a rotational force transmitting portion of a deformed shape.
The rotational force transmitting portion is provided with a diameter larger than that of the female screw portion and is formed continuously to the female screw portion. Therefore, from a necessity of working the rotational force transmitting portion, the crown head is formed by a head main body one end directed to a side of the case band of which is opened, and a cap constituting a part separate from the head main body, and the cap is mounted to close other end of the head main body.
According to the timepiece, the female screw portion is attachably and detachably brought in mesh with a male screw portion and the crown can be held so as not to be rotated carelessly by a mesh thereof. The rotational force transmitting portion is attachable and detachable to and from the rotational force receiving portion. That is, in the screw lock state in which the female screw portion is brought in mesh with the male screw portion, the rotational force transmitting portion is separated from the rotational force receiving portion. In a state of releasing the screw lock by releasing the mesh of the female screw portion and the male screw portion, in accordance with moving the crown head by an urge force of an elastic member, the rotational force transmitting portion is fitted to the rotational force receiving portion. Therefore, when the crown head is operated to rotate in a state of releasing the screw lock, the rotation is transmitted to the crown shaft by way of the rotational force transmitting portion and the rotational force receiving portion which are fitted together and the hand setting stem can be rotated (refer to, for example, JP-A-2005-127816 (paragraphs 0011-0055, FIG. 1-FIG. 5)).
According to the timepiece of Patent Reference 1, there is achieved an advantage of capable of lightly operating a screw locking operation since in operating to rotate to bring the female screw portion of the crown head in mesh with the male screw portion of the pipe in order to achieve the screw lock state, the hand setting stem is not rotated cooperatively therewith.
However, when the screw lock is released, during a time period after releasing the mesh of the female screw portion and the male screw portion, until the rotational force transmitting portion is engaged with the rotational force receiving portion, the crown head is not supported and there is a possibility of shaking the crown head. Therefore, there is a case in which the operation of the crown head becomes unstable and the rotational force transmitting portion cannot smoothly been gaged with the rotational force receiving portion. Further, by the same reason, in bringing the female screw portion in mesh with the male screw portion in order to constitute the screw lock state, when the crown head is unstable, there is a case in which the mesh cannot smoothly be carried out and when a user forcibly constitutes the mesh under the state, there is conceivable a concern of damaging the screw portion.
Further, according to the timepiece of Patent Reference 1, the female screw portion having a diameter smaller than that of the rotational force transmitting portion and being integral with the crown head is provided continuously to the rotational force transmitting portion. Thereby, when the rotational force transmitting portion having the deformed shape is formed on an inner side of the crown head, the female screw portion constitutes a hindrance against working of the rotational force transmitting portion. Therefore, working using a shaper cannot be carried out. Along therewith, punching cannot be carried out when working is carried out by using a press. In this way, working suitable for mass production performance cannot be carried out, and therefore, special devise is needed for working the rotational force transmitting portion and a concern of being difficult to work the rotational force transmitting portion accurately is conceivable.